The marital drama deals with questions of temptation, betrayal and defining infidelity - and Keira and her co-star Eva said there were no easy answers.

The movie is about a married couple struggling to confront temptation.

For Keira's character it's an old, never-quite-forgotten French love, while for her husband, played by Avatar star Sam Worthington, it's a work colleague played by Eva.

Their moral struggle plays out over the course of one night they spend apart, on the backdrop of hotel bars and trendy New York apartments.

Keira said the movie doesn't take a view on whether one is worse - physical infidelity or an unconsummated but highly emotional affair - and that she could not say.

"We discussed that a lot," the British actress said during a press conference in Rome. "Sometimes I went into it thinking the mental infidelity was worse, then we're shooting and I think, 'No, No, the physical's much worse. I come out and I have no idea."

The actress said the movie "provokes discussion" and credits it for not taking a moral standpoint or tell the viewers what to think. "This is a film that requires the audience to make their own minds up," she said, adding that all people at one point in their lives have faced the scenarios the characters find themselves in.

Eva said all relationships were different and there were a lot of grey areas.

"It's too black and white to say, 'No, this is worse than that,'" Eva said. "Maybe something that's acceptable in your teens or 20s is unacceptable in your 30s or 40s."

Horoscopes

Your Horoscopes by Russell Grant

Pisces:

Your income will get a big boost, thanks to an impressive work assignment. You will be very busy in the days ahead, which is beneficial. You have a tendency to rest on your laurels when you have lots of free time. A demanding schedule forces you to step up your game. If your energy starts to flag, make time for daily exercise. It seems counterintuitive, but moving your body can actually refresh you. Working with a partner is strongly advised. A collaborator will attend to practical matters.More